1. Field of the Invention
This invention generally relates to a hydraulic control system of an automatic transmission. More particularly, this invention relates to a control system of an automatic transmission provided with two oil pumps serving as sources of hydraulic pressure.
2. Description of the Prior Art
In recent years, an idling stop vehicle has been developed which automatically stops an engine to reduce the fuel consumption, the exhaust emission, the noise, etc. when the vehicle stops running and predetermined stop conditions are satisfied. In such a vehicle, the stop of the engine stops a main pump driven by the engine. Therefore, oil supplied to a forward clutch of an automatic transmission gets out of an oil channel to lower the hydraulic pressure. Thus, the forward clutch, which should be engaged in the forward driving, is disengaged at the restart of the engine. If the forward clutch is not quickly engaged at the restart of the engine, an accelerator pedal is operated in a neutral state so that the forward clutch is engaged while the engine is blowing up. This generates an engagement shock.
To address this problem, there has been developed the technique disclosed in Japanese Patent Application Laid-Open Publication No. 2000-46166. According to this technique, two pumps are used; a main pump and an assist pump. Driving the main pump supplies fluids, and when the main pump stops while an engine is stopped, the assist pump driven by the electric motor is singly operated to compensate the shortage of oil flow. This aims to ensure that the supply of working fluids to an automatic transmission is kept while controlling the battery power consumption to the minimum level.
According to the above prior art, however, the assist pump driven by the electric motor is operated while the engine is stopped. This consumes a large amount of power in reality. Particularly in a traffic jam or the like, the battery and the motor for driving the assist pump are overburdened.
It is therefore an object of the present invention to provide a hydraulic control system of an automatic transmission which has a main pump driven by an engine and an assist pump driven by an electric motor, the hydraulic control system which is able to supply necessary hydraulic pressure without burdening the electric motor or a battery to realize smooth driving even if the main pump stops to cause the assist pump to supply hydraulic pressure when an idling stop controlling operation is carried out.
The above object can be accomplished by providing a method for controlling an automatic transmission which comprises a hydraulic pressure source including a main pump driven by an engine and an assist pump driven by an electric motor, and an idling stop switch, the method comprising: detecting a vehicle speed, a steering angle and a brake operation; stopping the engine and the assist pump, when predetermined conditions for idling stop operation are detected according to the vehicle speed, the steering angle and the brake operation; and then driving a starter motor for starting the engine to cancel the idling stop operation and the assist pump, if the brake is not in operation, or the idling stop switch is operated to terminate the idling stop operation.
According to the present invention, when the engine is stopped due to the idling stop operation, the electric motor also stops driving the assist pump. This prevents the electric motor from continuing its operation while the idling is stopped. This enables the idle stop controlling operation without burdening the battery or the electric motor.
Further, the idling stop operation can be cancelled by operating the idling stop switch if desired. And when the idling stop operation is cancelled both the starter motor and the electric motor are actuated to restart the engine while supplying sufficient hydraulic pressure to the automatic transmission from the assist pump, thereby realizing smooth driving.
The above object can also be accomplished by providing a control system of an automatic transmission which comprises: a starter motor for starting an engine; a hydraulic pressure source having a main pump driven by the engine and an assist pump driven by an electric motor; idling stop control unit for outputting engine idling operation signal and idling stop signal to an engine control unit under predetermined idling stop conditions according to a vehicle speed signal detected by a vehicle speed sensor, a steering angle detected by a steering angle sensor, and a signal from a brake switch detecting whether a brake is operated or not; the control system comprising: an idling stop switch for switching an operation of the idling stop control unit between an idling operation and an idling stop operation; wherein if the idling stop control unit outputs an idling stop signal to the engine control unit, the assist pump as well as the engine are stopped; if the idling stop control unit receives an OFF signal from the brake switch or receives an idling stop control termination signal from the idling stop switch, the idling stop control unit outputs a cancellation command for canceling the idling stop operation to the engine control unit to drive the starter motor and drive the assist pump.
According to the invention, when the idling stop control unit stops idling the engine, the electric motor also stops driving the assist pump. This prevents the electric motor from continuing its operation while the idling is stopped. This enables the idle stop controlling operation without burdening the battery or the electric motor.
Further, since the control system of the automatic transmission has the idling stop switch that switches the operation of the idling stop control unit between the idling operation and the idling stop operation, it is therefore possible to cancel the idling stop operation even if the idling stop conditions are satisfied for the idling stop control unit. For example, if a driver desires to operate an air conditioner or the like while the idling is stopped, the battery will be overburdened by the operation of the air conditioner while the engine is stopped. To address this problem, the idling stop operation is canceled to run the engine, and this enables the operation of the air conditioner or the like without burdening the battery.
Further, if a cancellation command for canceling the stop of idling is outputted, both the starter generator for starting the engine and the electric motor for driving the assist pump are actuated to restart the engine while supplying sufficient hydraulic pressure to the automatic transmission. This realizes smooth driving.
According to one preferred form of the present invention, if the idling stop control unit outputs a cancellation command to the engine control unit, the electric motor for driving the assist pump is actuated a predetermined period of time before actuation of starter motor; and the predetermined period of time is determined to be longer for lower oil temperature and shorter for higher oil temperature.
Since the oil should be supplied to an oil channel to a clutch for restarting the vehicle, the assist pump is actuated a predetermined period of time before the actuation of the starter generator. More specifically, it may be impossible to ensure sufficient hydraulic pressure due to the viscosity resistance of the oil just after the actuation of the assist pump, because the viscosity of oil is high when the oil temperature is low. Therefore, as the oil temperature lowers, the predetermined period of time is increased so as to ensure sufficient hydraulic pressure.
According to another preferred form of the present invention, when an oil temperature is not higher than a predetermined temperature, the idling stop operation is prohibited even if the conditions for idling stop are satisfied.
If the oil temperature is low, the viscosity of the oil is high. In this case, it is impossible to supply sufficient hydraulic pressure to a transmission unit and more particularly to the forward clutch, etc. that require engagement pressure when the vehicle is started. This causes a starting shock and the like. To address this problem, the idling is stopped only when an oil temperature ensuring a certain viscosity is reached. This enables the stable idling stop controlling operation.
According to yet another preferred form of the present invention, the idling stop switch is a snap switch.
This makes it possible to switch the control state only by pressing one switch when the driver requires the controlling operation to stop or start. Basically, the idling stop control operation is automatically started when the driver operates the ignition key. Thus, the idling stop controlling operation automatically carries out or stops the idling operation. Accordingly, there are required two switching functions, one of which is for stopping the idling and the other is for executing the idling to satisfy the driver""s needs. By using the snap switch, however, it is possible to easily switch the control state by operating only one switch without requiring the driver to perform any complicated operations.
According to yet another preferred form of the present invention, a discharge circuit of the assist pump is provided with a relief valve that maintains a discharge pressure of the assist pump at a predetermined pressure or lower.
Even if a driving force is excessive at the restart of the engine, an advance clutch, etc. that is engaged at the start of the vehicle is prevented from being supplied with excessive hydraulic pressure and the vehicle is prevented from moving suddenly at the restart of the engine due to excessive engagement force generated by the excessive driving force. The predetermined pressure is not greater than an inherent discharge pressure of a main pump when the engine is idling.
According to yet another preferred form of the present invention, the idling stop control unit is provided with an electric motor control section that maintains a discharge pressure of the assist pump driven by the electric motor at a predetermined pressure or lower.
This prevents the discharge pressure of the assist pump from becoming excessive. Although a control program is added, a control program is added, but there is no need for adding new components such as a relief valve to thus reduce the cost.